For example, a company which produces color printed matter, such as a printing company, periodically measures the colors of the printed matter and adjusts the colors of a printing device which has printed the printed matter to maintain the quality of the printed matter. For this color adjustment of the printing device, for example, original image data called a color chart is printed by the printing device, and each color of each patch in this printed color chart is measured by a colorimetric device. Then, a color shift amount between the measured value of the color of each patch and the target value of the color of each patch is evaluated, and the colors of the printing device are adjusted according to this evaluation result.
The color chart is configured by including a plurality of color samples called the patches, and each of the plurality of the patches is often formed with a different color (hue, brightness, chroma) from each other and arrayed in a predetermined manner. There are various kinds of such a color chart. For example, there is a color chart of an aspect configured by arranging a plurality of quadrangular patches having various colors vertically and horizontally in a two-dimensional array. The color chart of this aspect further has various patterns including that each patch is arrayed so as to be in a random (random) color array depending on the contents to be evaluated and that each patch is arrayed so as to reduce changes in contrasting densities of patches adjacent to each other, like gradations. Accordingly, such a color chart is not only created by a user by using a color chart creating tool provided by a manufacturer of a colorimetric device, but also provided by a public institution. Thus, the color chart has quite various patterns due to differences in the shapes, arrangements, colorations and the like of the patches.
On the other hand, the number of colors used for the color adjustment of a printing device has been increasing year by year. Accordingly, the number of patches arranged in a color chart has also been increasing. Moreover, the size (area) of each patch is small.
Under these circumstances, it is becoming practically impossible to manually accurately align a measurement part of a colorimetric device with each patch to perform colorimetry. For this reason, an automatic system is desired to automatically measure a position of each patch and automatically align a measurement part of a colorimetric device with this measured position of each patch to measure the color of each patch. As one example of this system, Gretag-Macbeth AG has proposed, in the Patent Literature 1, a method of colorimetrically measuring a color chart by capturing a two-dimensional color image of a color chart desired to be measured, calculating a position of a patch with an image processing technique using a computer, and moving a colorimetric head to the determined position of the patch.
Incidentally, as described above, there are various kinds of color charts. One of the color charts includes not only a chart region where a plurality of patches exist, but also a normal image region where a normal image, in which, for example, a landscape, animals, plants, people, goods, characters (symbols) and the like are imaged, exists. Since the automatic patch position measuring method of automatically measuring the position of the patch disclosed in the Patent Literature 1 does not determine whether or not the patch belongs to the chart region, the method also measures the position of the patch in such a normal image region as a measurement subject when the method measures the color chart including the normal image region. Thus, the automatic patch position measuring method disclosed in the Patent Literature 1 may erroneously detect the position of the patch.